The present invention relates to a process for the manufacture of polyethylene, and in particular to a process by which the major part of the enthalpy decrease available between the polymerisation reactor and the separator in which the polyethylene is separated from the ethylene can be recovered.
It is known that because of the increasing cost of energy, reduction in energy consumption has become of primary concern in industry. Despite this, very little effort has hitherto been dedicated to reducing energy consumption in installations for the manufacture of polyethylene, in which the reaction takes place under a very high pressure which is generally above about 800 bars. The enthalpy decrease available between this reaction pressure and the separation pressure, which is generally below 400 bars, is not usually recovered. U.S. Pat. No. 3,649,208 describes a process for compressing a fluid which consists in using a plurality of powered means for compressing fluid to effect production of a product, in admitting fluid and at least one constituent to said powered means, in causing a reaction to occur between said one constituent and fluid to initiate formation of the product from a portion of the fluid, in supplying means with a portion of the energy stored in said compressed fluid for powering given means of said plurality, and in separating the product from the remaining fluid. This process does apply to the manufacture of polyethylene and discloses a turbine as an example of means supplied with a portion of the energy stored in the compressed fluid. However it makes it possible to provide only up to 50% of the energy required for compressing the fluid, and, furthermore, the practical means for carrying out this process in industry and the operating conditions of these means are not described. Finally, this process involves a well-known restriction which consists in using all the recovered energy inside the installation for the manufacture of polyethylene.